Research on Pulse TIG Welding Power Supply Based on ARM and CPLD

Literature Overview

This 2012 research by Liu Qiang and Song Yonglun from Beijing University of Technology investigates the design and implementation of a pulse gas tungsten arc welding (pulse TIG) power supply based on ARM microcontroller and Complex Programmable Logic Device (CPLD) technology. Published in the Welding Machine journal, this work represents an important advancement in welding power electronics, enabling precise control of welding parameters that are critical for high-quality welds in cladding, overlay, and pressure vessel fabrication applications. The development of intelligent welding power sources is essential for meeting the demanding requirements of modern manufacturing, particularly in industries where weld quality directly impacts safety and reliability.

Core Technical Points

Pulse TIG welding offers significant advantages over continuous TIG welding for many applications:

• Reduced heat input, minimizing distortion and HAZ width
• Improved penetration with lower average current
• Better control of weld pool geometry and bead profile
• Reduced spatter and improved arc stability
• Enhanced suitability for thin materials and cladding applications

The pulse TIG power supply described in this study utilizes:

• An ARM microcontroller for high-level control algorithms and parameter management
• A CPLD for real-time generation of pulse waveforms with precise timing
• Power electronics including IGBT or MOSFET inverters for high-frequency switching
• Feedback loops for current and voltage regulation

Key Technical Specifications of the Pulse TIG Power Supply

Control Architecture and Signal Processing

The control system architecture is hierarchical, with the ARM microcontroller handling high-level tasks and the CPLD handling real-time waveform generation:

Control Hierarchy

1. ARM Microcontroller (Top Level): Manages user interface, stores welding procedures, implements adaptive control algorithms, and communicates with external systems
2. CPLD (Middle Level): Generates pulse waveforms with nanosecond timing accuracy, implements current regulation loops, and interfaces with power stage
3. Power Stage (Bottom Level): IGBT/MOSFET inverter converts DC to high-frequency AC, rectifies to DC, and delivers controlled output current

The CPLD is particularly valuable for pulse waveform generation because it can produce complex pulse patterns (such as double-pulse, triple-pulse, or shaped pulses) with timing accuracy that would be difficult to achieve with software-based control alone. The pulse parameters—peak current, background current, pulse frequency, and pulse ratio—can be independently controlled to optimize weld quality for different applications.

Application to Cladding and Overlay Welding

Pulse TIG welding is particularly well-suited for cladding and overlay welding applications in bimetal product manufacturing:

For nickel-based alloy cladding (such as Inconel 625 or Hastelloy C276), pulse TIG welding allows precise control of the dilution ratio by adjusting the background current and pulse parameters. Lower background current reduces heat input to the base metal, while higher peak current ensures adequate penetration and bonding. The pulse ratio can be optimized to maintain a stable arc while minimizing thermal distortion.

Process Development and Optimization

Developing a welding procedure specification (WPS) for pulse TIG cladding requires systematic optimization of parameters. The following approach is recommended:

1. Initial parameter selection: Based on material thickness, desired cladding thickness, and joint geometry
2. Pulse parameter optimization: Vary peak current, background current, frequency, and ratio to minimize dilution while maintaining bond strength
3. Travel speed optimization: Balance productivity with cladding thickness and quality
4. Shielding gas optimization: Ensure complete protection of the weld pool and back side
5. Procedural qualification: Test the qualified procedure on production-representative joints

A typical optimization matrix for pulse TIG cladding might include:

Study Insights and Engineering Implications

The development of ARM and CPLD-based pulse TIG power supplies represents a significant step toward intelligent welding systems that can adapt to changing conditions in real time. For pressure vessel fabrication, this technology enables:

• More precise control of cladding thickness and dilution
• Reduced rework and scrap rates
• Improved consistency in automated and semi-automated welding operations
• Better integration with digital manufacturing systems and process monitoring

The use of CPLD for waveform generation is particularly advantageous because it allows for rapid changes in pulse parameters without the latency associated with software-based control. This is important for maintaining arc stability during transitions between different welding positions or when compensating for variations in joint fit-up. The ARM microcontroller provides the flexibility to implement advanced control algorithms such as adaptive control, expert systems, or data analysis-based optimization, although the study itself focuses on the hardware architecture rather than advanced software algorithms.